As an instant messaging service widely used by mobile and smart phones, Kakao talk® is being widely used, and recently, it launched Voice talk, which is an application offering free voice calls. For Voice over Internet Protocol (VoIP)-based services like instant messaging services or Voice talk, a dedicated application such as the KaKao application, which is used to send and/or receive instant messages or voice packets, needs to be installed in mobile terminals of both the sender and the receiver. The dedicated application sends and/or receives instant messages or voice packets using an MNO provided by a communication company, as shown in FIG. 1, and if the sender and the receiver sign up for different communication companies, instant messages or voice packets may be sent and/or received with different MNOs belonging to different communication services cooperating with each other.
That is, conventional instant messages or voice packets can be exchanged only when the same dedicated applications are installed on both the sender mobile terminal and the receiver mobile terminal.
To solve the problem with the dedicated application, Korean Patent No. 2001-0061989 proposed an instant messaging system, in which a sender uses a phone number of a receiver as an account to offer instant messages to the receiver. However, with the invention proposed by the Korean Patent No. 2001-0061989, only text can be exchanged by means of the phone number of the receiver as an account, but mobile VoIP (mVoIP)-based free voice calls cannot be provided.
At present, Kakao, which is an instant messaging service, is now providing Voice talk thus enabling fee voice calls, but Voice talk suffers from limitations that such services are only enabled among mobile terminals on which the same dedicated application is installed.